Processing of optically effective surfaces of spectacle lenses by material removal can be roughly divided into two processing phases, namely initially preparatory processing of the optically effective surface for producing the macrogeometry in accordance with prescription and then fine processing of the optically effective surface in order to eliminate preparatory processing tracks and obtain the desired microgeometry. Whereas preparatory processing of the optically effective surfaces of spectacle lens is carried out in dependence on, inter alia, the material of the spectacle lenses by grinding, milling and/or turning, in fine processing the optically effective surfaces of spectacle lenses are usually subjected to a precision-grinding, lapping and/or polishing process, for which purpose use is made of an appropriate machine. To that extent, in the terminology of the present application the term “polishing”, including expressions such as, for example, “polishing tool” or the like, is to embrace precision-grinding and lapping processes, in the example thus precision-grinding or lapping tools.
Manually loaded polishing machines in RX workshops, in particular, are usually constructed as “twin machines” so that advantageously two spectacle lenses of an “RX job”—a spectacle lens prescription always relates to a pair of spectacle lenses—can be subjected to fine processing simultaneously. Such “twin” polishing machines are known from, for example, documents U.S. Pat. Nos. 8,696,410 and 9,289,877, which disclose a related machine kinematics.
According to, for example, the last-mentioned document (see, in particular, FIGS. 1 to 5 thereof) such a polishing machine comprises a machine housing bounding a work space into which project two workpiece spindles, by way of which the two spectacle lenses to be polished can be driven by a rotary drive to rotate about substantially mutually parallel workpiece axes of rotation C1, C2. On the tool side, the polishing machine has a first linear drive unit by which a first tool carriage is movable along a linear axis X extending substantially perpendicularly to the workpiece axes of rotation C1, C2, a pivot drive unit which is arranged on the first tool carriage and which pivots a pivot yoke about a pivot setting axis B extending substantially perpendicularly to the workpiece axes of rotation C1, C2 and substantially perpendicularly to the linear axis X, a second linear drive unit which is arranged on the pivot yoke and by which moves a second tool carriage along a linear setting axis Z extending substantially perpendicularly to the pivot setting axis B, and two tool spindles each with a respective tool mounting section, wherein each of the tool mounting sections projects into the work space to be associated with a respective one of the workpiece spindles.
Each tool spindle has a spindle shaft on which the respective tool mounting section is formed and which is mounted in a spindle housing to be driven to rotate about a tool axis of rotation A1, A2, which housing in turn is guided in a guide tube to be capable of defined axial displacement in the direction of the tool axis of rotation. Whereas the spindle housings of the two tool spindles are flange-mounted on the second tool carriage, the guide tubes are mounted on the pivot yoke so that as a result the tool axis of rotation A1 or A2 of each tool spindle forms with the workpiece axis of rotation C1 or C2 of the associated workpiece spindle a plane in which the respective tool axis of rotation A1 or A2 is axially displaceable (linear axis X, linear setting axis Z) and tiltable (pivot setting axis B) with respect to the workpiece axis of rotation C1 or C2 of the associated workpiece spindle.
By virtue of the given possibilities of movement, the prior art polishing machine allows—with a compact construction—pairwise processing of spectacle lenses not only by a so-called “tangential polishing kinematic” in which the polishing tools axially adjusted (Z) together with the tool spindles are moved under a preset, but fixed, pivot angle (B) of the tool spindles in oscillation with relatively small strokes transversely (X) over the spectacle lenses, but also with a polishing kinematic in which the adjusted (Z) polishing tools during the oscillating transverse movement (X) thereof at the same time continuously pivot (B) so as to follow the surface curvature of the spectacle lenses, wherein the spectacle lenses and the polishing tools can be driven (but do not have to be at least as far as the polishing tools are concerned) in the same sense or opposite sense at the same or different rotational speeds about the axes of rotation (A1, A2, C1, C2) thereof.
To that extent, it is certainly advantageous that this polishing machine can be widely used. However, in the case of specific materials which are difficult to polish such as, for example, polycarbonate materials or high-index material it is still desirable to process with different polishing bases in order to reduce polishing times and/or achieve specific surface qualities, which in the afore-described prior art would require a change of polishing tools. The same applies if spectacle lenses to be polished in succession significantly differ in the geometry thereof (surface curvature, diameter). Tool change times thus required can indeed be significantly reduced for industrial production by use of automated tool changers with tool magazines, but this would be involve a substantial outlay on equipment.
What is desired is a device, which is constructed as simply and compactly as possible, for fine processing of optically effective surfaces of, in particular, spectacle lenses, the device being usable as widely as possible and thus allowing different processing strategies without requiring longer processing times.